Rungs on the aluminum ladder are often fabricated with square pipes jointed to the rails of the ladder; due to narrow pedal sides of the rungs, it is unsteady for the user to stamp on and falling caused by carelessness may happen easily. FIG. 3 shows a cross-section of the conventional rung, and it has a square pipe member (113′) with an upper plate-shaped pedal member (111′) and a lower plate-shaped pedal member extending outward from the upper and lower sides of the square pipe member (113′), respectively. The pedal members (111′, 112′) of the conventional rungs each provide only a single vertical support joining to the square pipe member (113′), and it is weak and unsafe for the user to step on.